Thank you and everyone for your help.
The letters were intercepted by the French and published in a two volume set which I am now translating and which is being posted on this site under "what's new." These letters should be posted soon.
Unfortunately, what we have is a French translation from the original German (done in 1807), with me transcribing the antiquated French and translating into English. The book itself has numerous typographical errors and seems to have been rushed into press, as the events described were only months old at times.
I think the original German letters would be fascinating to read, if only to know the authors, which for some reason, the publishers often did not include.